1. Field of the Invention
This invention relates to a flexible, energy absorbing orthotic device for high heel footwear and a method for its manufacture.
2. Background of the Related Art
One of mankind's most unique footwear designs has to be that of the ladies high heel shoe. By raising the heel higher than that of the natural foot angle, the woman's natural walking pattern is altered, resulting in higher impulsive loads on the musculoskeletal system. In an investigation utilizing small low-mass piezoelectric accelerometers attached to the skin surface of both tibial tuberosities, the heel and metatarsal strike acceleration values began to exceed the barefoot values in the heel height ranges of 1.75 to 2.25 inches. See, FIG. 8 which is a graph showing the acceleration values generated at the tibial tuberosities from the heel(H) and metatarsal(M) region by a ladies low heel shoe having a 0.2 inch heel with no insole; and FIG. 9 which is a graph showing the acceleration values generated from the heel(H), and metatarsal(M) region by ladies high heel shoes having a 2.6 inch heel with no insole.
The phenomena of the metatarsal strike exists in every type of human locomotion, such as walking, running, hopping, jumping, stair climbing, and the like. Not much attention has been paid to this phenomena, however, simply because there has been a lack of appropriate or accurate measuring techniques. It is true, that this second acceleration value is rather negligible during regular low heel or barefoot walking, which may be the reason that it has not been discussed in prior literature. However, with increasing heel height, the effect of the metatarsal strike becomes more and more profound. As shown in FIGS. 8 and 9, our measurements indicate that for a subject wearing a 2.6" heel, in addition to the conventional heel strike, a metatarsal strike of magnitude similar to that of a 0.2" low heel strike is observed. In practical or layman's terms, this means that when wearing a shoe with the aforementioned size heel, the human musculoskeletal system is subjected to approximately twice as much abuse as when walking barefoot, or, the damage induced on the musculoskeletal system is equivalent to that of when the subject is covering twice as much distance. The quantitative evaluation for the heel strike accelerations of 3.0 inch high heel shoes attained a level of over 175% that of flat shoe heel strike values. The force due to acceleration of the 3.0 inch high heel shoe was 130% greater than that of the barefoot case and the heel strike value for a 2.6" high heel was 125% greater than that of a flat shoe heel. Thus, the need to provide shock absorption in ladies high heel shoes is not only from heel strike initiated shock waves, but also from the metatarsal strike initiated waves.
Previously, shock attenuating insoles have been developed for men's, ladies' and children's footwear for use in boots, athletic shoes, and walking shoes U.S Pat. Nos. 4,187,621; 4,435,910; and 4,364,188 utilize closed cell foams and other materials having a high compression set which permanently deform under the load of the wearer, resulting in reduced comfort and effectiveness. These materials also do not absorb perspiration and/or odors and prevent aeration of the insole. Such materials include closed cell polyvinylchloride and polyolefin foams, closed cell neoprene foam and chemically blown natural and synthetic latex rubber foams.
U.S. Pat. Nos. 3,475,837; 2,350,362, 2,074,050; 1,724,349, 1,717,122; and 482,561 describe the construction of mens and ladies shoes with indentations in the heel portions. These shoes utilize soft or resilient pads positioned over and in the indentations for cushioning the user's heel. None of these designs is effective in reducing the acceleration due to heel and metatarsal strike initiated shock waves from ladies high heel shoes. Also, none of these designs attempt to reduce the acceleration resulting from metatarsal strike initiated shock waves.
U.S. Pat. No. 2,083,581 describes a women's high heel shoe with adjustable heel and metatarsal pads for modifying the sole conformation to better fit individual customers. The insole, heel and metatarsal pads are not intended and cannot reduce the acceleration force resulting from heel and metatarsal strike initiated shock waves because there are no energy attenuating materials incorporated in U.S. Pat. No. 2,083,581.
U.S. Pat. No. 4,335,530 describes mens and ladies high heel pumps with indentations in the heel and metatarsal regions. A pad protrudes from the midsole into an indention in the heel, and another pad in the metatarsal region of the midsole protrudes through the bottom of the sole near the metatarsal region, allowing the midsole to make contact with the ground, after impact by the sole. The midsole is made from a compressible, low density resilient foam material, as discussed above, such resilient materials are well known in the art as those which will not absorb the shock and resulting vibration of heel and metatarsal strike. In addition, the midsole construction of this patent requiring a fixed, nonremovable insole and also requires the insole to include a wear resistant layer below the metatarsal region for making contact with the ground.
U.S. Pat. No. 3,414,988 describes an insole for use in athletic shoes, made of a relatively thick resilient cushioning layer of porous plastic foam and at selected areas, a relatively thin, substantially non-resilient, shock absorbing ply of unicellular plastic foam.
U.S. Pat. No. 4,232,457 describes an orthotic insert comprised of a flexible plastic support member of incompressible material and a heel post made of a compressible, resilient material, such as an open cell natural sponge rubber. Resilient materials are well known in the art as those which will not absorb the shock and resulting vibration of a heel strike.
U.S. Pat. No. 4,541,184 describes the manufacture of a composite insole from an upper layer of flexible material bonded to a shock absorbing high density polyurethane material. This insole is unusually bulky and heavy due to the extension of the high density polyurethane material over the entire length of the insole, thus it cannot be inserted and comfortably worn in ladies high heel shoes. Several energy absorbent compositions are described in U.S. Pat. Nos. 4,101,704; 4,346,205 and 4,476,258.
Commonly assigned U.S. patent application Ser. No. 011,830 filed on Feb. 6, 1987 (Assignee: Polymer Dynamics, Inc., Lehigh Valley., Penn. 18001), describes a flexible resilient laminate and an insole fabricated therefrom by means of an overcharging process. There is no disclosure in Ser. No. 011,830 regarding the manufacture of an insole for ladies high heel shoes.
U.S. Pat. Nos. 4,581,187 and 4,674,204 describe the preparation of shock absorbing cushioned insoles. Neither of these patents, however, describe the manufacture and use of shock absorbing insoles for ladies high heel shoes. Accordingly, the insoles described therein are too large and bulky to be inserted and comfortably worn in ladies high heel hoes.
Many types of insoles have been proposed for various types of footwear. However, none have been able to reduce the amplitude of the heel strike initiated shock wave or the magnified metatarsal strike initiated shock wave by as much as the present invention while maintaining the classical shape of the ladies high heel shoe. All prior shock absorbing insoles occupy too great a volume to make their use practical and comfortable in a ladies high heel shoe. Likewise, the magnitude of the metatarsal strike initiated shock wave generated with the use of high heel shoes has heretofore been undisclosed.
Accordingly, it is an object of this invention to provide a shock absorbing insole for high heel footwear to reduce the amplitude of the heel strike shock wave, as well as the metatarsal strike shock wave, thereby reducing the risk of low back pain, debilitating joint disorders, osteoarthrosis, myositis of the calf, thigh and back and the like.
It is also an object of this invention to provide an orthopedically and biomechanically designed insole which offers cushioning for effective redistribution of the pressure between the sole of the foot and the shoe, henceforth, decreasing the possibility of callous and blister development.
Yet another object of the invention is to provide a functional, composite insole whose incorporation in high heel footwear will modify and dissipate the shock waves which propagate through human musculoskeletal system after each step.